Noble metals, such as ruthenium (Ru), platinum (Pt), iridium (Ir) and osmium (Os), have traditionally been used infrequently in semiconductor integrated circuits. Recently, however, these noble metals and/or the oxidized substances thereof have been studied for potential use as a lower or upper electrode of a capacitor. This is because the desired electrical characteristics for a capacitor may not be attainable by using polysilicon, which is commonly used as an electrode material when a material, such as Ta2O5, BST ((Ba, Sr)TiO3) or PZT((Pb, Zr)TiO3), that has a high dielectric constant is used as a dielectric film. Because Ru has a generally good leakage current characteristic and may be etched more easily than Pt, attention has been focused on the use of Ru film as the electrode of a capacitor.
Traditionally, sputtering methods have been used to form Ru films. In accordance with conventional sputtering methods, a Ru film may be densely formed and a generally good surface morphology may be achieved, thereby obtaining a Ru film having a generally good leakage current characteristic and a generally good resistance characteristic. One disadvantage to conventional sputtering methods, however, is that the Ru films formed thereby may provide poor step coverage. As a result, sputtering methods may be less desirable when forming an electrode having a three-dimensional shape, such as a cylinder shape or a fin shape.
CVD has been proposed for forming Ru films because films formed by CVD generally have better step coverage than those formed by sputtering methods. Specifically, in conventional CVD methods, Ru is deposited on a substrate or an interlayer dielectric layer using a vaporized Ru source gas and a reactant gas (i.e., a catalyzer) so that generally good step coverage can be achieved. Unfortunately, the surface morphology of a Ru film formed by CVD is typically worse than that of a Ru film formed by conventional sputtering methods. As a result, it may be difficult to obtain desired leakage current and resistance characteristic using conventional CVD methods. Consequently, there exists a need for improved CVD methods for forming Ru film.